Photovoltaic devices, such as amorphous silicon solar cells, described in U.S. Pat. No. 4,064,521, are capable of converting solar radiation into usable electrical energy. The energy conversion occurs as a result of what is well-known in the solar cell field as the photovoltaic effect. Solar radiation impinging on the solar cell and absorbed by the amorphous silicon generates electrons and holes. The electrons and holes are separated by a built-in electric field, for example, a rectifying junction in the solar cell. The separation of the electrons and holes creates the photocurrent of the solar cell.
The efficiency of the separation and collection of the holes and electrons by the built-in field is known as the collection efficiency. The collection efficiency or short circuit current as well as the fill factor of the solar cell can be improved, inter alia, by lowering the series resistance of the solar cell. This can be done by increasing the dark conductivity and photoconductivity of a layer of undoped (slightly N-type) or N-type hydrogenated amorphous silicon, thereby improving the performance of the solar cell. Thus, it would be highly desirable to increase the dark conductivity and photoconductivity of such solar cells.